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Date: Thu, 16 Oct 2008 21:15:05 +0400 From: Anton Vorontsov <avorontsov@...mvista.com> To: David Brownell <david-b@...bell.net> Cc: Andrew Morton <akpm@...ux-foundation.org>, lkml <linux-kernel@...r.kernel.org> Subject: Re: [patch] gpiolib: fix oops in gpio_get_value_cansleep() On Thu, Oct 16, 2008 at 10:06:21AM -0700, David Brownell wrote: > On Thursday 16 October 2008, Anton Vorontsov wrote: > > > - return chip->get(chip, gpio - chip->base); > > > + return chip->get ? chip->get(chip, gpio - chip->base) : 0; > > > > Why don't we check the .set in the gpio_set_value? Because > > we must always call gpio_direction_output()? > > Yes. The output driver needs to be explicitly enabled, > to avoid misbehaving electic circuitry. > > > > It is not exactly the > > same we work with the input direction.. is this documented anywhere? > > In Documentation/gpio.txt since the very first versions. > > See the section on "Spinlock-Safe GPIO access", where > special cases for reading the value of output GPIOs are > desribed. Other aspects are mentioned in other spots. > > For example, open drain signals -- as used with I2C and > other protocols -- only drive the "low" signal level, > and if code wants a "high" level it's got to verify that > nobody else is driving that shared line to low. By > reading it back, even though it's configured as output. I see. Much thanks for the explanations. -- Anton Vorontsov email: cbouatmailru@...il.com irc://irc.freenode.net/bd2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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